<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    .current{
        background: pink;
    }
    </style>
</head>
<body>
    <p id="test">hello world</p>
    <script>
    /* ele.setAttribute(attr,value) */
    var test=document.getElementById("test");
    test.setAttribute("style","color:blue");
    test.setAttribute("class","current");
    </script>
</body>
</html>